This invention relates to devices useful for imparting curl to tapes.
One difficulty often encountered in applying a flat length of tape to flat objects is that air can be entrapped between the tape and the flat smooth surface to which it is applied. Air entrapment is often undesirable since it can ultimately result in a non-uniform bond between the tape and the surface.
Entrapment of air as described above occasionally occurs when applying a length of flat tape comprising a particularly aggressive, pressure sensitive adhesive layer and is even more likely to occur in the event that the aggressive adhesive layer has an exposed surface which is free of surface irregularities and is glassy in nature. More particularly, a length of flat tape comprising an aggressive pressure sensitive adhesive layer will tend to adhere almost instantaneously over its entire length to a flat surface to which it is being applied once the tape is brought into contact with that surface. The consequence of this instantaneous adherence can be the undesirable of this instantaneous adherence can be the undesirable entrapment of air. In the event that the exposed surface of the adhesive layer is glassy, and once air has been entrapped, the air cannot escape even upon application of an external flattening force. This is in contrast to the situation in which surface irregularities exhibited by adhesive layers comprising tapes of other constructions (e.g. linered tapes) permit entrapped air to escape, particularly upon the application of a flattening force.
One commercial situation in which employment of flat, pressure sensitive tape may lead to an unsatisfactory product unless used on a liner is in the sealing of preformed openings in container ends with predetermined lengths of tape. Here it is highly desirable that no air be entrapped between the tape and the container end since, particularly upon exposure to elevated temperatures, entrapped air can lead to localized detachment of the tape and can ultimately result in contamination of the container's contents through exposure to the external environment or in corrosion of the top of the container end.
Conventional tape applying machines, such as those described in U.S. Pat. Nos. 2,684,240 (Lindsey), 2,990,081 (deNeui), 3,472,724 (Casey), 3,750,511 (Toensing) and copending application Ser. No. 041,629, filed May 23, 1979 and commonly assigned, typically require the use of linered tape when tape is applied to container ends. Linered tapes comprise tapes having a slightly irregular or rough surface on an aggressive pressure-sensitive adhesive layer which is covered with a release liner. The adhesive layer can be applied with these machines to container ends without significant entrapment of air. Linerless tapes which typically comprise glassy, aggressive pressure-sensitive adhesive layers and which are more economical than linered tapes are not generally compatible with applicating machines of the above type since air entrapment between the adhesive layer and the container end will likely occur.
Although curl may be imparted to strip materials such as tape by passing such materials over a sharp edge, such a curling means generally requires that the material be pulled over the sharp edge with great force and rapidity, conditions which many tape backings could not survive. In addition, the degree of curl imparted to a strip of material by such a curling means would typically be nonuniform over the length of the tape.